A centrifugal machine is an apparatus in which a specimen to be centrifuged is inserted into a rotor through a tube or a bottle, the rotor is coupled to the rotation shaft of a drive device made of a motor, and the rotor is rotated at a high speed to thereby centrifuge and refine the specimen. The rotation speed of the centrifugal machine varies depending on the use of the specimen to be centrifuged and refined; and, according to the uses of the centrifugal machines, generally, there are supplied various types of centrifugal machines the rotation speeds of which range from a low rotation speed of several thousands of rpm to a high rotation speed of 150,000 rpm or so. The types of rotors to be driven by the drive device also vary depending on the uses thereof; and, for example, there are known an angle rotor in which a tube hole is fixed, and a swing rotor in which a bucket with a tube loaded therein is rotated to thereby oscillate a rotor from a vertical state to a horizontal state. The rotors of these types can be mounted and removed as well as can be replaced through the rotation shafts of the drive devices that are used to rotate their associated rotors.
In these conventional centrifugal machines, as disclosed in the below-mentioned patent reference 1, the vibration of the drive device is dampened by supporting the drive device within a box member (a frame) through vibration preventive rubber which is referred to as a damper. Also, the vibration of the rotor, which is generated due to the imbalance of the rotor itself and due to the imbalance of the capacity, mass and the like of a specimen to be loaded into the rotor, is also transmitted to the drive device not only through the rotor but also through the rotation shaft, and is dampened by vibration preventive rubber (a damper) which supports the drive device.
The vibration involved with the centrifugal machine raises the following two major problems. The first is a self-excited vibration problem. As disclosed in the below-mentioned patent reference 2, owing to the imbalance of a specimen to be inserted into the rotor, or owing to a backlash between the rotation shaft of the rotor and a support cylindrical shaft, in the high speed rotation of the rotor, there can be generated a self-excited vibration having a low frequency component different from the rotation component of the rotor. This is referred to as self-excited vibration which is generated when the damping amount (internal damping amount) of the rotating structure member is larger than the damping amount (external damping amount) of the support-side vibration damping mechanism such as vibration preventive rubber. Also, the second problem is that, as disclosed in the below-mentioned patent reference 3, the damping characteristic (damping constant) of the vibration preventive rubber has temperature dependence. In other words, the temperature of the vibration preventive rubber can vary according to the temperature of the rotor chamber or according to the operating condition of the rotor (for example, it can vary in the range of 2° C.˜40° C.), and the damping amount of the vibration is greatly influenced by the temperature variation of the vibration preventive rubber.
To cope with these vibration problems, in Japanese Patent Publication Hei-7-26669 and Japanese Patent Publication 2005-111402, there is disclosed a technology which detects the vibration caused by the imbalance of the rotor. Also, in the Japanese Patent Publication 2006-7093, there is disclosed a technology in which there is provided an imbalance detect sensor and, when the output signal of the imbalance detect sensor provides a value equal to or higher than a given value, the drive device is caused to stop. Further, in the Japanese Patent Publication Hei-9-239293, there is disclosed a method for mounting a rotor onto a drive shaft in order to prevent the occurrence of the self-excited vibration; and, in Japanese Patent Publication 2004-64945, there is disclosed a technology in which, in order to compensate the temperature dependence of the vibration preventive rubber, a Peltiert element is used to control the environmental temperature of the vibration preventive rubber, thereby holding the damping characteristic of the vibration preventive rubber at the optimum value.
In the conventional centrifugal machines, the damping of the vibration generated in the vibratory system thereof depends almost on the provision of the vibration preventive rubber and, in order to increase the damping amount, the number of provision of the vibration preventive rubber is increased. However, to increase the number of provision of the vibration preventive rubber does not increase the damping amount (damping constant) but increases the spring reaction force that is given by the vibration preventive rubber. When the spring reaction force becomes large, the vibration to be transmitted from the drive device through the vibration preventive rubber (damper) to the box member increases. As a result of this, the box member becomes easy to vibrate, which makes it difficult to secure a sufficient damping amount. Further, as described above, since the damping amount of the vibration preventive rubber depends on the temperature thereof, it is necessary to compensate a reduction in the damping amount caused by the temperature dependence.